That's how the unit works, it keeps forcing the door against the stop until the resistance in the motor is detected to hit a preset value and it stops sending power. It's hard on equipment doing it that way, but that's what they decided to do rather than limit switches. I repaired mine with a gear type hose clamp. It's a tight fit and you have to line up the screw part in the right orientation or the screw part of the clamp will hit the moldings on the heater bog, but it works and it won't break again. And yep, I'm thankful every day that my passenger side hasn't failed. I'm so paranoid about the crappy setup that I usually don't adjust temp (leave it on high or low), just fan speed.
2004 Imola BMW ZHP
2006 Commander Limited Hemi QD2
"Bought, Not Built"